Definition of stable:
a. Resistant to change of position or condition; not easily moved or disturbed
b. Not subject to sudden or extreme change or fluctuation
c. Maintaining equilibrium; self-restoring

Using that definition stable would mean to fly straight with no change like I said. Being more stable would mean it has more resistance to change in its flight. Being less stable would mean have less resistance to change in its flight. So a drone would actually be less stable than a buzzz because it has a far more likelihood of deterring from its intended flight.
now terms like overstable are not actual words. and in the case of our sport overstable means to have more resistance to flying with the spin. thus having less turn and more fade. so a drone would be more overstable than a buzzz.
don't bastardize the language cause you don't truly understand the words you are using.

If you put a disc with spin imparted on it in a vacuum, what does it do? Gyroscopic precession makes it act like a Drone. Not a Buzzz. Which is why a Drone is more stable. A buzzz is still stable; it doesn't flip (the opposite of what discs want to do). It's just not as stable as an OS, which will never act against its nature (under human strength and worldly conditions).

Overstable, I don't even know what it would mean. Probably something like "creates its own spin".